Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41N—PRINTING PLATES OR FOILS; MATERIALS FOR SURFACES USED IN PRINTING MACHINES FOR PRINTING, INKING, DAMPING, OR THE LIKE; PREPARING SUCH SURFACES FOR USE AND CONSERVING THEM
  • B41N3/00—Preparing for use and conserving printing surfaces
  • B41N3/08—Damping; Neutralising or similar differentiation treatments for lithographic printing formes; Gumming or finishing solutions, fountain solutions, correction or deletion fluids, or on-press development

Definitions

• This invention relates to a plate cleaner for a lithographic printing plate.
• Lithography is a printing system taking advantage of the natural mutual repulsion between water and oils.
• the surface of a lithographic printing plate comprises areas which accept water and repel an oily ink, and areas which repel water and accept an oily ink.
• the former areas constitute non-image areas, and the latter areas constitute image areas. Accordingly, if the surface properties between these two areas is disturbed, for example, if the hydrophilic property of the non-image areas is deteriorated for some reason, inks are apt to adhere to such hydrophilicity-deteriorated areas to cause background stains.
• background stains are formed under various conditions.
• background stains are formed in the case where a lithographic printing plate is subjected to a burning-in treatment for the purpose of imparting high printing durability (i.e., run-length of printing) or in the case where the surface of a lithographic printing plate is allowed to stand in air without protection with a desensitizing gum.
• Such a plate cleaner conventionally includes a cleaner comprising an aqueous solution of sodium silicate.
• this plate cleaner despite of its very high desensitizing activity, is disadvantageous in that a part of an image is damaged or adhesion of an ink to image areas is deteriorated because of its alkaline property when it is applied to lithographic printing plates produced from presensitized lithographic printing plate precursors such as positively-working presensitized lithographic printing plate precursors having a light-sensitive layer composed of an o-quinonediazide compounds, as described, e.g., in Japanese Patent Publication No. 28403/68, U.S. Pat. No.
• negative-working presensitized lithographic printing plate precursors having a light-sensitive layer composed of a binder having an acid group and a diazo resin, and the like, that are developed with an aqueous alkaline developer.
• a plate cleaner using oxalic acid as disclosed in U.S. Pat. No. 3,489,561 has a weak desensitizing property and an activity to corrode a metal support. Therefore, when it is applied to commonly employed lithographic printing plates comprising an aluminum plate as a support, the hydrophilic layer provided on the support, for example, a layer formed by a surface treatment to render hydrophilic, as described in U.S. Pat. No. 2,714,066, is susceptible to destruction to cause stains. Therefore, such a plate cleaner is not adequate for metal supports.
• the printing plate surface is first treated with an ink remover (e.g., kerosene or hydrocarbon type solvents) to remove the ink, and then with a desensitizing agent.
• an ink remover e.g., kerosene or hydrocarbon type solvents
• the above-described plate cleaner is also used as a desensitizing agent after the removal of ink. This means that the treatment for cleaning the plate surface should be done over two steps. Therefore, an emulsion type plate cleaner having both functions, i.e., serving as an ink remover and also as a desensitizing agent, has recently been developed.
• An object of this invention is to provide a plate cleaner for a lithographic printing plate which has excellent effects to desensitize non-image areas and to remove or prevent stains without adversely affecting image areas.
• Another object of this invention is to provide a plate cleaner for a lithographic printing plate which effectively removes stains without damaging the hydrophilic surface of non-image areas.
• a further object of this invention is to provide a plate cleaner for a lithographic printing plate which exerts excellent effects to remove stains and to desensitize non-image areas, irrespective of the type of the printing plates.
• a still further object of this invention is to provide a plate cleaner for a lithographic printing plate which is easy to handle and inexpensive.
• the inventors have extensively investigated to develop a plate cleaner which is free from the disadvantage of reducing adhesion of an ink to image areas as encountered with a non-emulsion type plate cleaner comprising an alkaline aqueous solution while retaining a desensitizing ability possessed by said plate cleaner, and which is applicable to any type of lithographic printing plates.
• a plate cleaner comprising an aqueous solution containing a silicate and at least one surface active agent selected from the group consisting of cationic surface active agents and amphoteric surface active agents.
• the plate cleaner according to the present invention comprises an aqueous solution containing (a) a silicate, (b) at least one surface active agent selected from the group consisting of cationic surface active agents and amphoteric surface active agents, and optionally, (c) a nonionic surface active agent, and/or (d) an organic solvent.
• the silicate which can be used in the present invention includes those represented by the formula
• M represents an alkali metal, ammonium, or a quaternary ammonium (e.g., N(CH 3 ) 4 , N(C 2 H 5 ) 4 , N(CH 2 OH) 4 , N(C 2 H 4 OH) 4 , etc.); and n represents an integer of from 1 to 5.
• M represents an alkali metal, ammonium, or a quaternary ammonium (e.g., N(CH 3 ) 4 , N(C 2 H 5 ) 4 , N(CH 2 OH) 4 , N(C 2 H 4 OH) 4 , etc.); and n represents an integer of from 1 to 5.
• silicates include sodium silicate, lithium silicate, potassium silicate, rubidium silicate, cesium silicate, ammonium silicate, and the like.
• Water-soluble silicates are preferred, but water-insoluble silicates may also be used in the state of colloids in an aqueous solution.
• the above-described silicate is used in an amount of from 0.5 to 20% by weight, and preferably from 2 to 10% by weight, based on the total weight of the plate cleaner.
• the cationic or amphoteric surface active agent used in the present invention prevents deterioration of adhesiveness of an ink to image areas which is ascribed to swelling of a part of the image areas and the like, improves adhesion of an ink to image areas, and thereby prevents deterioration of printing durability.
• the cationic surface active agents which can be used in the present invention include a trimethyl type, a benzyl type, an amine salt type, an imidazoline type, an amide type, and the like.
• the amphoteric surface active agents which can be used in the present invention include an alkylbetaine type, an alkylimidazoline type, and the like.
• These surface active agents are used in an amount of from 0.01 to 10% by weight, and preferably from 0.05 to 5% by weight, based on the total weight of the plate cleaner.
• These surface active agents can be used individually or in combinations of two or more thereof.
• the nonionic surface active agent which can optionally be used in the present invention is effective to improve wettability of a plate surface and to remove a printing ink or make a printing ink distribution uniform, to thereby ensure the cleaning effect of the plate cleaner.
• nonionic surface active agent examples include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene fatty acid esters, glycerin fatty acid esters, oxyethylene-oxypropylene block copolymers, and the like.
• Nonionic surface active agents having an HLB (i.e., hydrophile-lypophile balance) value in the range of from 8 to 20 are particularly preferred in the present invention.
• HLB hydrophile-lypophile balance
• the organic solvent which can optionally be used in the present invention is effective to dissolve or swell an ink present in scratches generated in non-image areas of a lithographic printing plate, thereby promoting dispersing of the ink in the surface active agent.
• Organic solvents having a boiling point of from about 130° C. to about 300° C. are preferred in the present invention. Further, it is advantageous to select those organic solvents which are easily solubilized with the nonionic surface active agent used. It is particularly effective to use organic solvents which have water solubility of 10% by weight or less at ambient temperature (e.g., 20° C.), such as ethylene glycol dibutyl ether, ethylene glycol benzyl ether, ethylene glycol phenyl ether, methylphenylcarbitol, n-amyl alcohol, methylamyl alcohol, benzyl alcohol, methylcyclohexanone, cyclohexanol, cyclohexanone, butyl ethyl ketone, and the like. These organic solvents are used in an amount ranging from 0.1 to 5% by weight, and preferably from 0.3 to 3% by weight, based on the total weight of the plate cleaner.
• the plate cleaner in accordance with the present invention can be used to remove background stains of a lithographic printing plate which are formed in any stage from plate making through printing. It exhibits a high ability to remove stains and is free from various problems as encountered with conventional plate cleaners, such as reduction in printing durability, reduction in adhesion of an ink to a printing plate surface, and corrosion or damage of a hydrophilic surface of non-image areas.
• the plate cleaner according to the present invention may contain a nitrate, a sulfate, a phosphate, and the like in addition to the above-described components. It may further contain a wetting agent, e.g., glycerin, ethylene glycol, propylene glycol, butylene glycol, pentadiol, hexylene glycol, diethylene glycol, triethylene glycol, etc. It is also possible to color the plate cleaner with dyes and the like.
• a wetting agent e.g., glycerin, ethylene glycol, propylene glycol, butylene glycol, pentadiol, hexylene glycol, diethylene glycol, triethylene glycol, etc. It is also possible to color the plate cleaner with dyes and the like.
• the presensitized printing plate precursor was then exposed to light through a positive transparency bearing halftone-dot image, developed with a developer for a positive plate (DP-3, produced by Fuji Photo Film Co., Ltd.; 6-fold diluted with water), washed with water, and dried.
• DP-3 produced by Fuji Photo Film Co., Ltd.; 6-fold diluted with water
• Sample Plates A, B, C and D were treated according to the conditions shown in Table 1.
• sample plates were mounted on a printer "KOR" manufactured by Heidelberg Co. (West Germany) to carry out printing.
• Sample Plates A to C Prior to printing, Sample Plates A to C were treated with the above prepared plate cleaner for about 30 seconds, and the plate cleaner was wiped off with water-containing sponge.
• normal prints with perfect adhesion of an ink could be obtained after 7 or 8 prints from the start of printing in each case. No background stains were formed even after producing 30,000 prints. Comparing between Sample Plates A to C and Control Sample Plate D not having been treated with a plate cleaner, no difference was observed in terms of size and wear of halftone dots on the image areas. Further, Sample Plates A to C produced normal prints with respect to ink adhesion, formation of stains, and the like as compared with Control Sample Plate D.
• a light-sensitive solution having the following formulation was applied onto the above prepared aluminum support to obtain a negative-working presensitized lithographic printing plate precursor having a light-sensitive layer coated at 1.8 g/m 2 on a dry basis.
• the resulting printing plate precursor was exposed to light through a negative transparency bearing half-tone dot image, developed with an aqueous developer having the following formulation, washed with water, and dried.
• Sample Plates E, F, G, and H were treated in the same manner as described for Sample Plates A to D in Example 1, respectively.
• clear prints were obtained after 10 to 20 prints from the start of printing with Sample Plates E to G, indicating no substantial difference from the Control Sample Plate H not having been treated with the plate cleaner.
• Example 2 The same procedures as described in Example 1 were repeated except that the four test plates were designated as Sample Plates I, J, K, and L, respectively, and the plate cleaner having the formulation shown in Table 2 was used. For comparison, a plate cleaner containing no cationic or amphoteric surface active agent was tested in the same manner. The results obtained are also shown in Table 3.
• Tables 2 and 3 show that the plate cleaners according to the present invention are excellent in ability to remove stains. It can also be seen that application of the plate cleaner of the present invention does not substantially influence adhesion of printing ink in image areas. To the contrary, the printing plate treated with the comparative cleaner required 25 to 40 prints from the start of printing for achieving satisfactory adhesion of an ink and was susceptible to influences on printing durability (about 20-30% reduction in printing durability), although the comparative plate cleaner had a high ability to remove stains.

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• Printing Plates And Materials Therefor (AREA)
• Manufacture Or Reproduction Of Printing Formes (AREA)

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Cited By (27)

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Citations (9)

• 1984
  • 1984-01-12 JP JP59004016A patent/JPS60147395A/ja active Granted
• 1985
  • 1985-01-09 US US06/690,067 patent/US4576743A/en not_active Expired - Lifetime

Patent Citations (9)

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